1. Field of the Invention
The present invention relates to technical fields of a crosstalk removal apparatus for removing a crosstalk of adjacent tracks included in a reproduction signal of a main track based on the reproduction signal of the main track of an information recording medium and reproduction signals of the one and other adjacent tracks, and an information reproduction apparatus which uses the crosstalk removal apparatus to reproduce recording information from the information recording medium with the tracks formed therein.
2. Description of the Prior Art
Large-capacity information recording media such as a DVD have a problem that a reproduction signal of a main track to be reproduced is influenced by a crosstalk from adjacent tracks and a reproduction quality is deteriorated. Therefore, a crosstalk canceller has been noted in which three light beams are used to simultaneously reproduce three tracks disposed adjacent to one another, a pseudo crosstalk is obtained from the reproduction signals of the adjacent tracks, the crosstalk is subtracted from the reproduction signal of the main track, and the crosstalk is removed.
In general, since three light beams for use in the crosstalk canceller are emitted at predetermined intervals in a track tangent direction, a time difference is generated in the reproduction signal of each track. Therefore, it is necessary to delay the reproduction signal of each track by a predetermined delay amount, cancel the time difference and match phases of the respective reproduction signals before the crosstalk is removed.
On the other hand, the delay amount of the reproduction signal of each track does not always indicate a constant value, and fluctuates with an elapse of time depending on a fluctuation of a laser wavelength and properties of an information recording medium. Therefore, in order to delay the reproduction signal by an appropriate delay amount in the crosstalk canceller, it is necessary to control the delay amount to be optimum in the crosstalk canceller, and to compensate for the fluctuation of the delay amount with time. For example, a jitter value corresponding to the reproduction signal is detected, and the delay amount may be set such that the jitter value is minimized. That is, the crosstalk increases in a deviating state of the delay amount. Therefore, if the delay amount is set in minimizing the jitter value, the crosstalk can be removed in an optimum manner.
In recent years, rewritable information recording media such as a DVD-RAM have increasingly spread. For example, a land groove recording system is used in the DVD-RAM, and recording information can repeatedly be written both in a groove track and a land track. Moreover, the land and groove tracks of the DVD-RAM are subjected to wobbling beforehand in a constant period, and are used as criteria of a timing control.
Usually with the information recording media such as the DVD-RAM, a situation is assumed in which recorded and unrecorded tracks are present in a mixed manner. Therefore, the recording information is not necessarily recorded in the adjacent tracks during reproduction of the main track. When the adjacent tracks are already recorded, the jitter value changes based on the crosstalk, and the delay amount of the crosstalk canceller can therefore be controlled as described above. On the other hand, when the one and other adjacent tracks are unrecorded, the crosstalk does not occur and therefore the jitter value does not change. Even when the jitter value is detected as described above, the delay amount cannot appropriately be controlled with respect to the crosstalk canceller. As a result, when the recorded track suddenly appears in the adjacent track, a reproduction operation is performed in the deviating state of the delay amount of the crosstalk canceller. A problem is that the crosstalk cannot adequately be removed and the main track is not reproduced.
The present invention has been developed in consideration of the above-described problem, and an object thereof is to provide a crosstalk removal apparatus and information reproduction apparatus which detect a wobble signal and thereby obtain an optimum delay amount even with an unrecorded adjacent track, and can remove a crosstalk with a high precision during reproduction of a recordable information recording medium.
The above object of the present invention can be achieved by a crosstalk removal apparatus of the present invention which removes a crosstalk of one adjacent track and the other adjacent track included in a reproduction signal of main track based on the reproduction signal of the main track as a reproduction object of an information recording medium and reproduction signals of the adjacent tracks. The crosstalk removal apparatus is provided with: a crosstalk removal device which delays the reproduction signals of the main track and the adjacent tracks by predetermined delay amounts corresponding to respective reproduction time differences, extracts the crosstalk from the reproduction signals of the one and other adjacent tracks, and removes the crosstalk from the reproduction signal of the main track; a wobble signal detection device which detects wobble signals corresponding to a wobbling applied to the main track and the adjacent tracks; and a delay amount control device which obtains optimum delay amounts based on a phase relation of the detected wobble signals, and controls the delay amounts to be set with respect to the crosstalk removal device.
According to the present invention, when reproduction signals of a main track, one adjacent track and the other adjacent track are generated during reproduction of an information recording medium, these reproduction signals are delayed by predetermined delay amounts and subsequently a crosstalk is removed. In this case, a wobble signal. corresponding to a wobbling applied to each track is detected, and the delay amount is controlled such that the delay amount obtained based on a phase relation of the respective wobble signals is set. The wobbling performed beforehand on the recordable information recording medium is used, and therefore an optimum delay amount can always be obtained without obtaining a jitter value, even when the adjacent tracks are unrecorded. Moreover, since a period of the wobble signal is accurate, the delay amount is controlled with a high precision, and the crosstalk by the adjacent tracks can securely be removed.
In one aspect of the present invention, the delay amount control device detects phase differences between the wobble signal as a criterion and the other wobble signals, and obtains the optimum delay amounts corresponding to the phase differences.
According to this aspect, a criterion is determined among a plurality of detected wobble signals, and a phase difference among the respective wobble signals is detected so as to control the delay amount as described above. Therefore, the accurate delay amount can be obtained in accordance with the wobble signal which has an accurate period.
In another aspect of the present invention, the delay amount control device generates binarized signals of the wobble signals, obtains pulse widths corresponding to deviations of phases between the binarized signal of the wobble signal as the criterion and the binarized signals of the other wobble signals and detects the phase differences.
According to this aspect, the plurality of detected wobble signals are binarized, and a phase difference between the binarized signals is obtained as a pulse width, so that a relatively simple digital circuit can be used to control the delay amount as described above.
In further aspect of the present invention, the delay amount control device detects the phase differences between the wobble signal as a criterion and the other wobble signals, and obtains said delay amounts so that the phase differences are brought close to zero.
According to this aspect, a crosstalk removal device uses the delayed reproduction signal to detect the phase difference as described above, and controls the delay amount in such a manner that the phase difference is brought close to zero. Therefore, a fluctuation of the delay amount with time is constantly fed back and corrected, and the optimum delay amount can steadily be kept.
In further aspect of the present invention, the delay amount control device detects a zero cross of the wobble signal as the criterion, and uses the zero cross as a timing criterion to detect the phase differences.
According to the present invention, to detect the phase difference between the wobble signal as the criterion and the other wobble signals, a zero cross of the wobble signal is detected. In this constitution, the phase difference is detected by a simple processing and the delay amount can be controlled as described above.
The above object of the present invention can be achieved by an information reproduction apparatus of the present invention which reproduces recording information from an information recording medium with tracks formed therein. The information reproduction apparatus is provided with: a reproduction device which generates respective reproduction signals based on reflected lights obtained in irradiating a main track as a reproduction object, one adjacent track, and the other adjacent track with light beams at predetermined intervals in a tangent direction; a crosstalk removal device which delays the reproduction signals of the main track and the adjacent tracks by predetermined delay amounts corresponding to respective reproduction time differences, extracts a crosstalk from the reproduction signals of the one and other adjacent tracks, and removes the crosstalk from the reproduction signal of the main track; a wobble signal detection device which detects wobble signals corresponding to a wobbling applied to the main track and the adjacent tracks; and a delay amount control device which obtains optimum delay amounts based on a phase relation of the detected wobble signals, and controls the delay amounts to be set with respect to the crosstalk removal device.
According to the present invention, when reproduction signals of a main track, one adjacent track and the other adjacent track are generated during reproduction of an information recording medium, these reproduction signals are delayed by predetermined delay amounts and subsequently a crosstalk is removed. In this case, a wobble signal corresponding to a wobbling applied to each track is detected, and the delay amount is controlled such that the delay amount obtained based on a phase relation of the respective wobble signals is set. The wobbling performed beforehand on the recordable information recording medium is used, and therefore an optimum delay amount can always be obtained without obtaining a jitter value, even when the adjacent tracks are unrecorded. Moreover, since a period of the wobble signal is accurate, the delay amount is controlled with a high precision, and the crosstalk by the adjacent tracks can securely be removed.
In one aspect of the present invention, the delay amount control device detects phase differences between the wobble signal as a criterion and the other wobble signals, and obtains the optimum delay amounts corresponding to the phase differences.
According to this aspect, a criterion is determined among a plurality of detected wobble signals, and a phase difference among the respective wobble signals is detected so as to control the delay amount as described above. Therefore, the accurate delay amount can be obtained in accordance with the wobble signal which has an accurate period.
In another aspect of the present invention, the delay amount control device generates binarized signals of the wobble signals, obtains pulse widths corresponding to deviations of phases of the binarized signal of the wobble signal as the criterion and the binarized signals of the other wobble signals and detects the phase differences.
According to this aspect, the plurality of detected wobble signals are binarized, and a phase difference between the binarized signals is obtained as a pulse width, so that a relatively simple digital circuit can be used to control the delay amount as described above.
In further aspect of the present invention, the delay amount control device detects the phase differences between the wobble signal as a criterion and the other wobble signals, and obtains the delay amounts so that the phase differences are brought close to zero.
According to this aspect, a crosstalk removal device uses the delayed reproduction signal to detect the phase difference as described above, and controls the delay amount in such a manner that the phase difference is brought close to zero. Therefore, a fluctuation of the delay amount with time is constantly fed back and corrected, and the optimum delay amount can steadily be kept.
In further aspect of the present invention, the delay amount control device detects a zero cross of the wobble signal as the criterion, and uses the zero cross as a timing criterion to detect the phase differences.
According to the present invention, to detect the phase difference between the wobble signal as the criterion and the other wobble signals, a zero cross of the wobble signal is detected. In this constitution, the phase difference is detected by a simple processing and the delay amount can be controlled as described above.